Cigarette smoke (CS) is the primary cause of COPD, the fourth leading cause of death in the US. CS-induced oxidant stress causes endothelial cell (EC) apoptosis, and there is growing evidence that apoptosis of alveolar wall cells plays a role in the development of emphysema. The overall objective of this proposal is to understand mechanisms of CS-induced lung EC apoptosis and emphysema. Our previous studies on carboxylmethylation of small GTPases indicated that inhibition of RhoA GTPase activity causes focal adhesion complex (FAC) disruption and lung EC apoptosis. We present preliminary data indicating that CS extract (CSE) disrupts FAC via oxidative stress, causes EC apoptosis, and decreases RhoA activity. Aim 1: We will determine if oxidant- mediated RhoA inactivation causes CSE-induced loss of FAC and apoptosis of pulmonary EC. Our previous studies also demonstrated that EC apoptosis occurs despite activation of the unfolded protein response (UPR) when ER molecular chaperones are decreased. Our preliminary data indicate that CSE activates a UPR component, eIF2a, which was also activated in emphysematous lungs of mice exposed to CS. Aim 2: We will determine if UPR is first activated upon CSE exposure and ultimately defective after prolonged oxidative stress in pulmonary EC. Autophagy is a protective process, markers of which have been demonstrated in lungs of COPD patients. Our preliminary data demonstrate increased expression of autophagy markers in lung endothelial cells exposed to CSE and in lungs of mice exposed to CS. Aim 3: We will determine if autophagy is activated upon CSE exposure and ultimately defective after prolonged oxidative stress in pulmonary EC. The proposed studies will enhance understanding of the pathogenesis of emphysema and may result in develop of new therapeutic approaches to this devastating disease.